Before a facsimile image is transmitted from an originating facsimile machine to a terminating facsimile machine, the originating and terminating facsimile machines send messages between the machines to negotiate transmitting and receiving modes for transferring facsimile data. Such transmitting and receiving modes specify a set of parameters that are agreed upon prior to transferring facsimile data. These parameters may include a data bit rate, a page size, the number of pixels per line, the number of lines per page, and whether or not any field characters are added to a line so that the terminating facsimile machine has time to print each line. However, for wireless systems implementing analog facsimile sessions as described in IS-707-A.7, a problem arises concerning the quality of the transport channel across the RF interface. The prior art, and the IS-707-A.7 standard itself, addresses the areas of rate fallback and rate mismatch using system configuration parameters found in a Maximum Rate Message (MRT). The MRM broadcasts a top limit of data rates for analog facsimile sessions to all terminals in the system. However, such a system is required to be designed to a fixed maximum throughput limit that would be expected for all terminals in a particular coverage area.
Other prior art is found in the T.30 procedures for Document Facsimile Transmission in the General Switched Telephone Network Specification, which is propagated by the International Telecommunication Unit (ITU). In the T.30 procedures, a channel quality monitoring procedure is implemented through a Training Check (TCF) message, which acts as a sounding board to the transport circuit's ability to support the Bit Error Rate (BER) performance for a selected analog modem (i.e. V.17, V.29, or V.27ter). If the circuit cannot support the rate used by the TCF, then the terminating facsimile machine can assert a Failure to Train (FTT) message causing the originating facsimile machine to reduce its facsimile transfer rate. However, this technique cannot be applied to the situation concerning the quality of the transport channel across the RF interface because the analog modem is not involved in the transfer of data across the subject RF channel. Therefore, there is a need for an improved method and apparatus for modifying facsimile data transfer rates based upon varying bit rates of a transport medium.